Timothy W. Ellis

Deformation-processed wire prepared from gas-atomized Cu-Nb alloy powders

Wires have been fabricated by deformation processing of precursor billets that were prepared from alloy powders made by high-pressure gas atomization (HPGA) of a copper-20 vol pct niobium melt. The powders were classified, and a larger size fraction, whose microstructure consisted mainly of 0.4-µm-diameter Nb dendrites, was fabricated into the precursor billet by powder metallurgical techniques. The deformation-processed wire prepared from the powder alloy billet gave significantly increased strengths at a given level of deformation strain over similar material produced by consumable arc casting. This may be attributed to the smaller initial Nb dendrite size of the alloy powder used for the precursor billet. However, the electrical conductivity of the powder material at a given strength level was significantly lower than the arccast material. The cause of the reduction of the conductivity is uncertain, and possible reasons are discussed.

A high specific strength, deformation-processed scandium-titanium composite

A 59{percent} Sc{endash}41{percent} Ti deformation-processed metal-metal composite was produced by rolling to a true strain of 2.3 at 873 K followed by cold rolling to a total true strain of 3.6. Rolling reduced the original eutectoid microstructure to lamellae of {alpha}{endash}Sc and {alpha}{endash}Ti with average lamellar thicknesses of 150 nm (Sc) and 120 nm (Ti). The cold-rolled material had an ultimate tensile strength of 942 MPa and a specific strength of 259 J/g. The Sc matrix was oriented with the {l_angle}0001{r_angle} tilted 22{degree} from the sheet normal direction toward the rolling direction, an unusual texture for an HCP metal with a low c/a ratio, which suggests Sc may deform primarily by basal slip. {copyright} {ital 1999 Materials Research Society.}

Noncontaminating plasma arc sprayed crucible coatings for containing molten ceramic oxides

A study was performed to assess the suitability of several plasma arc sprayed coatings applied to graphite crucibles for melt processing AI2O3ZrO2, AI2O3 Y2O3, and AI2O3 ceramics. Coatings of W, Ta over W, and Re over W were evaluated. Pressed compacts of AI2O3 ZrO2, AI2O3Y2O3, and AI2O2 were each placed in refractory metal-coated graphite crucibles and heated to 2040,2150, and 2200 ‡, respectively. Compatibility of the coating/ceramic oxide systems was evaluated by optical and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and combustion chromatography. The Ta over W coating system was chemically nonreactive with all three molten oxides studied.

Studies on the optimization of deformation processed metal metal matrix composites

A methodology for the production of deformation processed metal metal matrix composites from hyper-eutectic copper-chromium alloys was developed. This methodology was derived from a basic study of the precipitation phenomena in these alloys encompassing evaluation of microstructural, electrical, and mechanical properties. The methodology developed produces material with a superior combination of electrical and mechanical properties compared to those presently available in commercial alloys. New and novel alloying procedures were investigated to extend the range of production methods available for these material. These studies focused on the use of High Pressure Gas Atomization and the development of new containment technologies for the liquid alloy. This allowed the production of alloys with a much more refined starting microstructure and lower contamination than available by other methods. The knowledge gained in the previous studies was used to develop two completely new families of deformation processed metal metal matrix composites. These composites are based on immissible alloys with yttrium and magnesium matrices and refractory metal reinforcement. This work extends the physical property range available in deformation processed metal metal matrix composites. Additionally, it also represents new ways to apply these metals in engineering applications.